They dont really go bad, its more like they get cranky from not using it.
I bet service guys just remove it and clean it then either install used one back or if on warranty they will order you a new one and have yours for somebody else.
However, if you push them to limits and have them in service for many years at some point they will need maintenance. usually is getting grease inside the actuator or when you bash them on rocks magnets will crack.
Another item is plug getting screwed because branch had ripped the wire.
If you have trouble and you are:
1. On warranty - then go to dealer
2. Outside warranty - remove it clean it, grease it and called it good.